This invention relates generally to the art of computer aided holography and holographic computer graphics, and more particularly to methods comprising the use of numerical and optical techniques to generate holograms from a computer model of any object.
Holograms are constructed by recording the interference pattern of a coherent object bearing beam and a coherent reference beam. The image of the object is usually reconstructed by directing the same coherent reference beam at the holograms.
Image-plane or focused-image types of holograms are constructed with an image of the object located either very close to or straddling the holographic plate. These holograms have the desirable property that, in reconstruction, the chromatic coherence requirement is relaxed, thus improving the white-light viewing of the holograms.
In practice, it is often impossible to place the hologram recording plate very close to an actual object, and impossible for the plate to be straddled by most objects. Various methods have been used to position an image of the object reconstructed from a hologram at or about the holographic plate. Early focused-image holograms are disclosed by Rosen in his article, "Focused-Image Holography with Extended Sources," published on page 337 of Applied Physics Letters, Vol. 9, No. 9, November 1966. The hologram is constructed by placing an image of the object onto the holographic plate by means of a lens system. This technique is simple, but the maximum field of view is limited by the practical f-number of the available lenses.
A common technique for making image-plane holograms without field of view constraints is to employ a two-step holographic method. A conventional hologram, H1, is first made of an object, and then a real image is reconstructed from it. A second holographic plate is positioned coincident with the real image to make a second, image-plane hologram, H2. Such a two-step technique is disclosed in various forms in U.S. Pat. Nos. 4,339,168, 4,364,627, and 4,411,489. In one form, a hologram consists of a cylindrical array of lenticular holograms, each made from a different viewpoint of the object. The image is reconstructed in the center of the cylinder. A second, focused image hologram may be made by positioning a hologram recording plate at the center of the cylinder, through a real image reconstructed from it, in a second step.